1. Field of the invention
The present invention relates to a contact-type developing method for developing a static latent image using a single-component non-magnetic toner.
2. Prior art
Conventional developing methods for developing static latent images using toners are divided roughly into two main classes. One is a two-component type developing method using a two-component developer essentially consisting of a non-magnetic toner and a carrier. The other is a single-component type developing method using a single component developer essentially consisting of a magnetic toner. Various improvements in connection with the two-component type and single-component type developing methods have been proposed.
However, the developing method using the two-component developer has the following drawbacks as compared with the developing method using the single-component developer:
(1) there is a need for a toner density sensor to control the ratio of the toner and the carrier;
(2) the life of the developer is short; and
(3) a mixer for mixing the developer must be handled with care and a large developing machine must be utilized.
The single-component type developing method using a magnetic toner has the following disadvantages:
(1) an electrostatic charge element must be formed as a sleeve or a blade and has less electrostatic charge stability and capacity as compared with a carrier;
(2) there is a need for a precision developing machine to produce a uniform magnetic brush; and
(3) the magnetic toner has fewer transferring, fixing, and environmental properties, and produces more damage to the photo-conductor than a non-magnetic toner.
In order to overcome the disadvantages described above and provide a small developing machine, the developing methods using single-component non-magnetic developers (toners) have been considered extremely efficient and attractive, and some of these have been practical.
The developing methods using single-component non-magnetic developers are roughly divided into two types: one is a contact-type developing method using single-component non-magnetic developers for developing a static latent image on a photo-conductor by contacting a developing roll which carries a toner with the photo-conductor. The other is a non-contact type developing method using single-component non-magnetic developers for developing a static latent image on a photo-conductor by virtue of flying a toner provided on a developing roll onto the photo-conductor which is adjacent to the developing roll with a gap.
The non-contact type developing method using single-component non-magnetic developers has an advantage in that the mechanical load exerted on the toners is smaller than in the contact-type developing method, since the toners are triboelectrically charged by only charging member. However, in the non-contact type developing method, the toner-flying properties tend disadvantageously to depend on the environmental conditions.
On the other hand, the contact-type developing method using single-component non-magnetic developers has an advantage in that good developing properties are exhibited. In the contact-type developing method, the mechanical load exerted on the toners is considerably greater than in the non-contact type developing method since not only a frictional force generated by the difference between the peripheral speeds of the photo-conductor and the developing roll, but also a triboelectric charging force caused by the charging member during the formation of a thin layer of toner on the developing roll is exerted. Therefore, one of the most important points associated with the contact-type developing method using single-component non-magnetic developers is that the toners not be fused to the triboelectric-charging member and the photo-conductor. In addition, another important point is that the photo-conductors and the developing roll not be cracked. In order to obtain a toner which will undergo reduced binding to the developing roll or the photo-conductor, one method which is effective is the use of a material having a high transition temperature as the binder resin used in the toner. However, this alone is not satisfactory.